I am building a rocket from scratch with three fins. It has been a long
time since I had to lay out three fins and I don't recall how to do this.
I will be building the motor mount with the fins attached first and then
sliding the slotted body tube over if that matters.
Any suggestions on getting the fins spaced out evenly?
Brian Elfert
Make a template by rolling a strip of paper around the tube, and marking
the point of overlap. Unroll it, and the marks are the circumference of the
tube. Measure, divide by 3, put back on tube, mark each fin position.
Brett
A firestarter grain ignited and pressed against it.
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Jerry
I assume you're trying to amke an Estes style fin marking template for your
tube. And it's not one of the MR sizes covered by the really useful yellow
Estes marking guide templates.
There's a nice trick you can do here. If you use LINED notebook paper, with
the lines running horizontal, then after removing it from the tube lay a
ruler at an angle on the paper so it crosses a multiple of 3 lines. Draw
that line. The intersections with the lines that are the multiples of 3 mark
your fin locations. You can use the lines as guides and fold creases at
those locations for a perfect marking template.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD"
>>> To reply, remove the TRABoD!
Unfortunately, in my case the rocket is much too big for lined notebook
paper unless someone has a notebook with 36" long pages.
I figured out what I am going to do. I calculated the circumference of
the centering rings and divided by 3. I am going to take a piece of
string the same length as the circumference and mark it where the fins
should go. I will wrap this around the centering rings and mark the fin
locations.
This will get my fins within 1/2 inch and that is good enough for the size
rocket I am building.
Brian Elfert
Pi times D = Circumference.
Cut a strip of paper this long.
Divide by three for three fins. Draw lines at those measurements.
Wrap around tube like Estes style fin marking guide.
Hopefully you know what to do from that point on.
I used my handy laser level. Put tube horizontal on flat surface, set
laser to draw horizontal line, and trace one line. Then use the paper
strip method to create other two lines using the first line as an
index.
Brian Elfert wrote:
notebook
Cool! A brilliant and innovative way to cheaply, and easily; perform
the classic drafting technique of dividing a line segment into "x"
equal segments.
Stand the tube up on a large sheet of paper, and draw around the
tube, marking its circumference on the paper. Remove the tube.
Draw a couple of straight lines that each intersect the circle in
two places.
Draw new lines perpendicular to each of these original lines,
centred on each line. Use a compass placed at the line / circle
intersections to draw little intersecting arcs on either side of
the lines, which you can then connect to form the perpendiculars
centred on these lines without measuring anything.
These new perpendicular lines will intersect at the centre of the
circle. Using a protractor, mark out and then extend three
lines, 120 degrees apart, from the centre of the circle.
Put your motor tube back on the original circle, and transfer to
it the locations of the three lines that are 120 degrees apart.
Using a piece of angle stock, extent these lines up the motor
tube, as your fin guides.
This same technique can be used to locate and mark the fin slots
for your airframe.
The paper you were drawing on makes a good visual fin guide when
you glue the fins on. If drawn on thicker stock you can cut out
the circle and the extended fin lines to make a template that can
be slid onto the tube and over the fins to keep everything
aligned while the adhesive sets.
...Rick
Give me a break. I would rather have them perfect, but 1/2" off won't be
noticeable on a large rocket.
The most important thing is to have the fins straight up and down.
Brian Elfert
And it's such an old trick, I can't even remember for sure where I learned
it from. Maybe my dad, maybe someone else, but I've been using it for a LONG
time, longer than many rocketeers have been alive.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD"
>>> To reply, remove the TRABoD!
Brian Elfert wrote in
news: snipped-for-privacy@corp.supernews.com:
Now I'm just a simple cardboard and balsa jockey, but seems to me you
can do this job with a piece of string and marker. No calculation, no
ruler.
Take the string, wrap it around your centering ring, clip it or mark the
length. There's your circumference of a value that you need not be
concerned about.
Take the string and fold the length that represents the circumference
into equal thirds. (letter z collapsed down on itself) Mark the two
bends with the marker.
Wrap the string around the ring and mark the start, and where the two
marks that were at the folds are on the ring. Do the same with the 2nd
and subsequent rings.
Seems simple to me. Just increase the number of equal string folds for
any number of fins you want.
ScottE - Engineers Know the Math, but Make the Jig
Use a compass... 120 degrees apart for 3 fins... not too hard... you don't
need to have the whole thing laid out on 360 degrees... you only need
baseline to 120 degrees... mark and spin the can just once... easy.
~ Duane Phillips.
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